1. Field of the Invention
This invention relates to organopolysiloxane compositions which are curable to elastomers and also relates to the use of such elastomers as sealants.
2. Background Information
Organopolysiloxane compositions which cure to elastomeric solids on exposure to water are well-known. Such compositions have found wide application as sealing materials for a variety of structures to which they may be applied and allowed to form elastomers merely by exposure to atmospheric moisture. Typically, such compositions comprise a polydiorganosiloxane and a crosslinking agent for the polydiorganosiloxane, for example, an alkoxy silane, an acetoxy silane, or an amino silane. In addition, the compositions may also contain one or more catalysts, fillers, pigments, adhesion promoters, and other ingredients. Examples of such curable compositions are those described in British Pat. Nos. 862,576; 905,364; 920,020; 962,061; 975,603; 1,035,492; and 1,071,311.
One important application of the above-described curable composition is their use as sealants in the building industry. For such applications, for example, in the fabrication and installation of glazed units, the cured elastomer should adhere strongly to both glass and the structure in which the glass is mounted. The elastomer should also have a relatively low modulus of elasticity which would permit it to adapt to the relative movement between the glazing and the structure due to the effects of temperature variation, wind, and other stresses. These requirements of adhesion and low modulus are sufficiently important that certain countries have established national standards relating to the use of sealants in glazing and building joint applications. For example, there exist in West Germany standards identified as DIN 18540 for building joints and DIN 18545 for glazing, which specify certain requirements as to adhesion and modulus of elasticity.
One type of curable composition which can be employed as a glass-bonding material is that based on a silanol-terminated polydiorganosiloxane and an oxime silane crosslinking agent, see for example British Pat. No. 1,468,467, Example 3. Such compositions have good curing characteristics in that they cure at an acceptable rate and do not produce corrosive substances during the curing process. However, they provide elastomers of relatively high modulus and having generally poor adhesion to glass and other substrates found in the building industry. We have not discovered that the modulus of such elastomers can be reduced and the adhesion thereof to, e.g. glass improved if there is incorporated into the elastomer-forming compositions certain complexes of titanium.
British Pat. No. 1,255,587 discloses compositions which are curable to elastomers on exposure to water and which comprise a diorganopolysiloxane possessing a silicon-bonded hydroxyl group in each of the terminal units and an organosiloxane having three monovalent hydrocarbon radicals, optionally-substituted, attached to one silicon atom and three groups Y attached to the other, Y being for example acyloxy, amino, aminoxy, aminoalkoxy, or oxime. The compositions may contain, as an optional ingredient, condensation catalysts for instance dibutyltin dilaurate and organosiloxy titanium compounds.
British Patent Application No. 2,002,405, published Feb. 21, 1979, discloses compositions curable to elastomers at room temperature and which contain inter alia, an organopolysiloxane having terminal silicon-bonded hydroxyl or hydrolyzable groups and a silicone-containing crosslinker having at least three hydrolyzable groups, e.g. alkoxy groups, acetoxy groups, amino groups, and ketoxime groups. The compositions optionally contain a curing catalyst examples of which are the metal salts of carboxylic acids, certain titanium compounds, amines, and amine salts. It is stated in the said application that the catalyst varies according to the hydrolyzable groups present. Example 1 discloses the use of a metal (tin) carboxylate as catalyst in compositions containing an alkoxy silane crosslinker. In Example 3, a composition crosslinked by way of an alkoxy silane contains a titanium chelate, as catalyst. There is no disclosure of a composition comprising a silanol-terminated polydiorganosiloxane, an oxime silane crosslinking agent and a titanium chelate. Example 2 of British Patent Application No. 2,002,405 relates to a composition containing an oxime silane but no catalyst is employed therein.